In electroerosion machining processes, it is well recognized that the machining medium plays important roles. These roles include the function as an electrical-discharge medium, the flushing of machining products and the cooling action. While the electroerosive machining medium has commonly made use of a hydrocarbon such as kerosene conventionally to fulfill these requirements, such a liquid is disadvantageously inflammable, involving the danger of a fire. Now, as an alternative thereto, water is widely in use, especially with a traveling-wire EDM machine. While a water liquid when distilled provides fairly well the required functions as the electroerosive machining medium, it leaves much to be desired as to its abilities to gain stock removal, machining stability and precision when comparison is made with a conventional inflammable hydrocarbon liquid.